Satellites are usually launched with their solar arrays stowed against the spacecraft sidewalls to fit within the launch vehicle. In this configuration, most of the power from the solar array is not available because there is no exposure to the sun. However, usually an outboard portion of the solar array is stored so that it's outward facing end produces some power from whatever sunlight reaches it during the initial phase, also known as "transfer orbit" (i.e., transfer from the as-launched orbit to the preferred mission orbit).
Solar arrays on satellites generally have three phases of operation. The first phase is the stowed configuration, in which the solar panels of the array are folded, concealed and compacted into a small area that accommodates fitting the satellite into the launch vehicle's cargo space. For maneuvering purposes, the solar panels are maintained in a stowed position until the satellite is properly placed in its final orbit. The time between launch of the satellite and it reaching its final orbit is generally referred to as "transfer orbit." The second phase of operation is deployment of the solar panels once the satellite is comfortably situated in it's destination orbit. The last and third phase constitutes the deployed panels at the end of the satellite's useful life.
Typically, the size of solar arrays are designed for their end-of-life (EOL) voltage and power requirements to meet the minimum voltage and power requirements of the satellite's electrical operation bus. That is, the maximum EOL power output of the solar array should meet the minimum power requirements of the satellite's electrical operation bus. The present method of meeting this EOL requirement necessarily means some degree of over-design at the BOL (beginning-of-life). Therefore, to provide sufficient EOL voltage the design will produce as much as twenty-five percent (25%) excessive voltage output at the BOL. Since standard satellite power regulation electronics operate at a constant voltage, the excessive voltage differential is wasted during BOL operation.
Solar cells are also temperature dependent devices and their running temperature depends on satellite orbit location and solar array geometry. At EOL, a deployed solar array operates at about 50.degree. C. which goes into the design analysis to meet the satellite minimum voltage requirement. Thus, during transfer orbit with the solar array not yet deployed and held tightly against the spinning satellite, as described above (typical stowed configuration) the solar array operates at about -20.degree. C. This 70.degree. C. temperature difference (-20.degree. C. to +50.degree. C.) further exacerbates the voltage differential noted above. The BOL voltage can be as much as sixty percent (60%) above the constant operating voltage required. This effectively amplifies the mismatch between the satellite constant voltage required and the voltage supplied leaving as much as a third or more of the voltage that cannot be traversed.
Therefore, one object of the present invention is to optimize solar array performance throughout the life of a satellite mission.
Another object of the present invention is to optimize solar array performance so as to provide maximum power output that matches the satellite's operation bus voltage during transfer orbit operation.
An object is also to optimize solar array power performance by selectively isolating non-contributing sections of a solar array to maintain the maximum power output of the stowed, BOL solar array.
A solar array power output is optimized as another object of the present invention by isolating a subsection of the solar array during transfer orbit operation and then connecting the subsection in series with another section to provide maximum power output that matches the power of the satellite operating bus at deployed EOL.
The solar array power output is optimized by connecting a subsection of the solar array through a switching device that automatically connects the subsection to the full array upon deployment of the solar panel of a satellite. Preferably, the switching devices are passive elements such as bypass diodes connecting sections of a solar array to the satellite's operating bus.